Cellular transforming genes have been identified in various human malignancies by DNA-mediated gene transfer using mouse NIH/3T3 cells as recipient. The db1 oncogene was detected as a transforming gene of human diffuse B-cell lymphoma. By molecular hybridization, db1 lacks detectable homology to other cellular or retroviral oncogenes. Intensive studies on the functions of number of transforming genes and their encoded proteins are beginning to reveal a close relationship between basic control signals governing cell transformation and normal cell proliferation. Therefore, it is of great interest to study the structure and functions of the protein encoded by a novel human oncogene, such as db1. We have identified a protein of about 66,000 daltons as the product of db1 oncogene. Preliminary subcellular localization studies revealed that P66 is a cytoplasmic protein distributed between cytosol and membrane fractions. Moreover, P66 is a phosphoprotein with phosphorylation being specific to serine residues. The present studies propose to pursue the characterization of P66 with a long term goal to understand its role in cellular transformation. Initial studies are aimed at characterizing the biosynthesis, precise subcellular localization and native configuration of db1 P66 which are pivotal to the understanding of its function. P66 phosphorylation will be characterized further to evaluate the regulatory effects of various growth factors and pharmacological agents. One of the aims of the studies presented here also includes the identification of the normal homologue of db1 P66. A comparison of the properties of normal db1 protein and P66 should provide information about the mechanisms of its acquired transforming potential. Furthermore, the distribution and levels of db1 protein will be evaluated in human neoplasms.